The present invention relates to methods for adjusting an interval or gap between two parallel arranged, plate-shaped objects and exposure methods using the same, and gap adjusting apparatuses and exposure apparatuses. More specifically, it relates to a method for detecting a proper gap between a mask and a wafer in a proximity exposure apparatus which exposes a desired pattern by radiating light onto the wafer through the mask arranged in close proximity to the wafer, an exposure method for exposing while using the above to arrange the mask and wafer such that they have a predetermined gap, a gap determination apparatus, and an exposure apparatus.
One example of apparatus that needs to keep two plate-shaped objects located in parallel at a predetermined gap is a proximity semiconductor exposure apparatus that locates a mask in a close proximity to a wafer, radiates light through this mask, and exposes a pattern created on the mask onto the wafer.
For a semiconductor integrated circuit fabricated by using such a semiconductor exposure apparatus, higher density and higher throughput has been promoted, and along with this, it has been demanded to form an integrated circuit with a narrow line width and a fine pattern. Accordingly, a semiconductor exposure apparatus is required to have high throughput as well as high resolution. It is also demanded for multiple exposure operations in which multiple circuit patterns are overlaid above one wafer to put multiple exposure positions in place with high precision. Further, use of a shorter wavelength of exposure light has been promoted for higher resolution, and thus an exposure apparatus using an X-ray light source has been developed. FIG. 16 shows a typical plan view of an example of such a conventional X-ray exposure apparatus.
This X-ray exposure apparatus includes a wafer chuck 94 that holds a wafer 93, and a mask chuck 91 that holds a mask 92 in parallel to and close to the wafer 93. The wafer chuck 94 is supported on a fine adjustment stage 95 that adjusts its position in XYZ-directions finely, and the fine adjustment stage 95 is further supported on a rough adjustment stage 96 that adjusts its position in XY-directions roughly. The mask chuck 91 is supported on a bottom surface of the mask chuck base 97 that is located opposite to the wafer chuck 94. An X-ray light source (not shown) is installed above the mask chuck base 97, and an opening is provided on the mask chuck base 97, through which an X-ray is radiated from top to bottom almost vertically.
An X-ray emitted from the X-ray light source is radiated, through the mask 92, onto the wafer 93 to which resist has been applied, thus exposing the resist. In exposing the wafer 93 using a specified pattern formed on the mask 92, the resist is exposed and this pattern is transferred. By removing exposed or unexposed part of the resist that has been exposed by the specified pattern, a semiconductor circuit of the specified pattern is created.
In order to expose a specified pattern at a specified position on the wafer 93, the above described exposure apparatus uses the rough adjustment stage 96 and fine adjustment stage 95 for locating the wafer 93 at a specified position relative to the mask 92 and performing an exposure operation there.
At this time, a gap between the mask 92 and wafer 93 needs to be correctly adjusted. This is because a radiated X-ray, which is irradiated in an almost vertical direction but not completely as shown in FIG. 17, has divergent and convergent angles to some extent, thus being directed to a direction slightly away from the vertical direction. In other words, since the X-ray propagating direction shifts from the vertical direction, the pattern on the mask 92 is exposed onto the wafer 93 at a position slightly away from vertically right under the pattern. This shift becomes larger as the gap between the mask 92 and the wafer 93 becomes wider. Therefore, if the gap fluctuates, there arises a change in exposure position (i.e., run-out error).
This exposure-position shift is problematic especially when different exposure apparatuses are used to overlay and form multiple semiconductor circuit patterns onto one wafer 93. For example, as shown in FIG. 17, when two exposure apparatuses, such as exposure apparatuses A and B which have different gaps between the masks 92 and wafers 93, are used to expose two circuit patterns, there arises a shift amount shown by RE between the two circuit-pattern exposure positions. As a result, two circuit patterns do not match well, possibly causing a defective semiconductor device.
One known, conventional method for setting a gap to be a predetermined amount between the mask 92 and wafer 93 to contact the mask 92 and wafer 93 once, making the gap in that state to be 0, and then moving the wafer 93 in a direction z by a predetermined amount. However, this method is likely to damage the mask 92 and wafer 93, cause foreign particles to be stuck between them after contacting them, and negatively affect the fine adjustment stage 95 by causing an unnecessary force to be applied to it by the contact.